A 19-year-old Thai woman presented with progressive ataxia and generalized tonic-clonic seizures. Later on, she developed status epilepticus. Blood was tested by molecular DNA analysis which showed A8344G mitochondrial DNA mutation associated with myoclonic epilepsy with ragged-red fibers (MERRF). We confirmed this finding in other members of this family. This is an interesting case report in Thailand of MERRF identified to have A-->G transition mutation at nucleotide 8344 of mitochondrial tRNA(lys) gene without ragged-red fibers from histopathologic studies of muscle. Molecular genetic analysis in suspicious cases of mitochondrial disorders is necessary for proper management and genetic counseling.